TekSIP is a SIP Registrar and SIP Proxy for Windows. TekSIP supports UDP, TCP, TLS and WebSocket (IPv4 & IPv6) transports. TLS and Secure WebSocket are supported in only commercial editions. TekSIP complies with RFC 3261, RFC 3263, RFC 3311, RFC 3581 and RFC 3891. It supports NAT traversal and ENUM. Please see technical details about NAT traversal in Readme. You can select IP address to be listened and alternative SIP endpoints for outgoing calls. You can also log session details into a log file and monitor active registrations and sessions in real-time. You can monitor number of active registrations and sessions using Windows Performance Monitor (Perfmon.exe). TekSIP can redirect calls to alternate endpoint when called endpoint is unavailable (Off-line, busy...). Active SIP session can be terminated via GUI. TekSIP has a Presence Server (SIP/SIMPLE based). TekSIP also supports UPnP IGD specification. If installed behind UPnP supported Internet gateway device (ADSL router e.g.), TekSIP automatically detects if it is behind a new NAT gateway and the external IP address. All outgoing requests manipulated for NAT traversal. You do not need to add manual reverse mappings for SIP and RTP protocols. TekSIP has also a built-in STUN server. TekSIP supports auto provisioning of IP phones based on SUBSCRIBE / NOTIFY PnP mechanism. TekSIP can optionally act as a B2BUA for incoming 3xx SIP responses. TekSIP can also act as a RTP Proxy and record audio streams if RTP proxy enabled. SP edition provides SRTP <-> RTP interworking. Recorded audio streams are saved in wave format can be played using TekSIP Manager. TekSIP can act as a WebRTC media and signaling gateway for SIP based WebRTC softphones. This enables WebRTC softphones to make calls to and accept calls from legacy SIP systems. RADIUS Authentication (RFC 2865) and Accounting (RFC 2866) are supported. RADIUS authorization is available in only SP edition of TekSIP. TekSIP accepts RADIUS disconnect requests as specified in RFC 5176.